Temporary Over Voltage (TOV) is a situation where voltage of a transmission grid increases above its nominal voltage. This may occur, for example, due to switching off large loads or one of the transmission lines. When the voltage at a wind turbine becomes too high, it may result in large current flowing into the converters of the turbine and damaging the components therein. Therefore, it is common for wind turbines to disconnect from the grid when the grid voltage increases above a certain threshold or when the current flowing into the converters becomes too high.
However disconnection from the grid is no longer desirable as more grid codes require wind farms to remain connected to the grid during a TOV event. Wind turbines having converters may have some capability to consume reactive power, and hence such turbines may individually monitor the grid voltage (or stator voltage or voltage at the primary or secondary side of the turbine transformer). If the turbine has detected a TOV event, it controls its converter to consume reactive power in order to ride through the TOV event.
Grid code requirements are usually stipulated at the wind farm level and not at the turbine level, and wind farms are expected to comply with the grid code requirements at a point of common coupling (PCC) between the wind farm and the grid. As each wind turbine attempts to ride through the TOV event on its own, there is no coordinated effort at the wind farm level. Hence there is no guarantee that the wind farm is able to remain connected to the grid during such TOV event.
Hence it is desirable to have a coordinated way of handling TOV event at a wind farm level.